So in fact there’s a specific process for coming to prophecy that’s comprised of a number of steps, some of which are quite open and above- board, and others that are rather arcane and only open to initiates.
But it would seem to be exceedingly important that a prophet knew that he was being communicated to by G-d. After all, there have been false prophets who have wreaked a lot of havoc.
For while Moses taught us at one point that “G-d your L-rd will raise up for you a prophet like me from your midst, from your brethren. Listen to him” (Deuteronomy 18:15), there are nonetheless other things to be said.
For we’re taught later on that “if a prophet, or one who foretells by dreams, appears among you and announces to you a miraculous sign or wonder, and … he says, ‘Let us follow other gods’ — gods you have not known — ‘and let us worship them,’ you must not listen to the words of that prophet or dreamer” (Deuteronomy 13:1-3). And we’re told that if “a prophet who presumes to speak in My name anything I have not commanded him to say, or … speaks in the name of other gods, (he) must be put to death” (Deuteronomy 18:20).
And so the overarching principle behind prophecy, as Ramchal depicts it here is that, “the prophet is absolutely sure that G-d’s Glory has appeared to Him” in the course of his revelations. That is, the prophetic experience would have to be so patently real and lucid that the prophet knows that he hadn’t been deceived, and that he didn’t imagine anything to have happened. He had to be sure that he’d indeed been communicated with by G-d. Of course a prophet didn’t come to that from the first; but that was the ultimate outcome of true prophecy.
Rabbi Yaakov Feldman has translated and commented upon “The Gates of Repentance”, “The Path of the Just”, and “The Duties of the Heart” (Jason Aronson Publishers). His works are available in bookstores and in various locations on the Web.